Wednesday, July 11, 2007

Whaling made penguins switch to krill

This article from Nature is pretty interesting... check out the whole thing here.

Ancient eggshell fragments show that Adélie penguins living in Antarctica switched from eating fish to krill around the time that humans began hunting seals and whales. The finding suggests that when humans removed krill-eating predators the penguins exploited the resulting shrimp surplus. Steven Emslie of the University of North Carolina in Wilmington, and William Patterson of the University of Saskatchewan in Saskatoon, analysed more than 220 fossil eggshell pieces ranging from 100 to 38,000 years old, and compared them with samples from modern nests. By comparing the proportion of certain forms of carbon and nitrogen in the shells with the proportions found in fish and krill, the researchers could tell what the birds had been eating. Emslie expected to find changes in diet matching climate change. Instead, the penguin menu remained biased towards fish until about 200 years ago, when the birds switched to krill. Recent global warming and the rise in krill fisheries has reduced krill stocks and could be contributing to the decline in Adélie penguin populations on the Antarctic Peninsula, says Emslie. The study is published in the Proceedings of the National Academy of Sciences1. Dietary switch From 1793 to 1807, an estimated 3.2 million seals were taken from the Southern Ocean. The resulting crash in the seal population — including the Antarctic fur seal Arctocephalus gazella, which fed primarily on krill — caused the industry to collapse.
This implies a huge dietary response.

Keith Hobson, Canadian Wildlife Service, Saskatchewan.
Whaling took off in the 1800s and continued until the mid-twentieth century, eventually depleting baleen whale populations by more than 90%. It's estimated that the combined harvest of seals and whales resulted in more than 150 million tonnes of extra krill each year. Krill is an attractive food for penguins because it is high in protein and tends to travel in swarms. "The birds can capture lots of high-energy prey in a short time," says Emslie. "This implies a huge ecological dietary response by the penguins in relation to some change in their environment," says Keith Hobson of the Canadian Wildlife Service in Saskatchewan. But the reasons behind this switch are less obvious, he says. "Abundance of a secondary food item does not necessarily explain this unless it was accompanied by a reduction in fish," says Hobson. "Why does it matter that krill became more abundant to a predator that previously happily made eggs from fish?"

Tiger Sharks Keep Seagrass Tidy

So I have heard of this before, and haven't actually seen the scientific article, but this is pretty cool none-the-less, from Discovery news. I thought when I had heard about this through the grapevine, it was sea turtle grazing that tiger sharks were controlling, but dugongs also makes sense, plus they can have a higher grazing impact. This article is a couple months after an article in nature about shark fishing leading to higher skate and ray populations that could be devastating to benthic shellfish populations. You can read about that article here, although it isn't the actual Nature article. Both show the importance of large apex predators on coastal ecosystems and gives credence to those who want to try and shut down shark fishing tournaments.

July 11, 2007 — Australian tiger sharks keep a tidy lawn for their marine neighbors by controlling where local herbivores can nibble, according to a study published in the current issue of Animal Behavior.

The discovery adds to the growing list of ways in which sharks benefit ecosystems worldwide. In seagrass communities in particular, countless other creatures depend on the presence of sharks.

"Seagrasses form the foundation for many near-shore marine ecosystems," lead author Aaron Wirsing told Discovery News. This is the case in Western Australia's Shark Bay, where seagrass is "nourishing and sheltering a host of invertebrates and fishes that, in turn, support top predators like sharks."

Wirsing, a researcher in the Department of Biological Sciences at Simon Fraser University, and his colleagues studied how the presence of tiger sharks specifically affected the feedings of dugongs — large aquatic mammals that somewhat resemble their manatee relatives.

Dugongs spend much of their day chewing on seagrass.

Through catch, tag and release methods, the scientists calculated tiger shark predation rates on dugongs.

Working under the auspices of the Shark Bay Ecosystem Research Project with funding from the National Geographic's Expeditions Council, the researchers focused their efforts on tiger sharks at least 10 feet long. Only adults that size are large enough to take on a chunky dugong.

The gentle herbivores prefer to eat segrass in the middle of patches. Growth is lush there and packs more of a nutritional punch due to the presence of extra organic carbon. Escaping from hungry sharks is difficult from these interior areas, however.

Wirsing and his team found that when large tiger sharks were around, dugongs instead chose to feed around seagrass meadow edges. The grass is not as tasty or nutritious at the edges, but the location allows escape to deeper water if predators are near.

By indirectly controlling where dugongs feed, tiger sharks keep the seagrass mowed down at all areas.

"Dugong grazing can certainly hold seagrass growth in check," Wirsing explained.

If left unchecked, however, the herbivores would simply eat all of the seagrass.

"That's where tiger sharks come in," Wirsing explained.

Both tiger shark and dugong populations are at dangerous lows in many places, because of human influence.

People often fear tiger sharks, since they have attacked people in the past, but George Burgess, director of the University of Florida's International Shark Attack File, attributes the attacks to tourist recklessness. He said tourists may often "bring their aquatic recreation to places known to be sharky without asking natives about good and bad places."

World Conservation Society biologist Tim Davenport said the dugong situation is just as bad. He explained that "dugongs are now critically endangered" in certain regions, such as in Tanzanian waters, primarily due to a combination of fishing net entanglement and habitat destruction.

Thursday, July 05, 2007

Thousands of rubber ducks to land on British shores after 15 year journey

This article is out of the Daily Mail, a British newspaper. This is pretty cool, knowing where this cargo of rubber duckies was lost, knowing how long each one took to reach their destinations, allows oceanographers to cheaply learn alot about ocean currents. Nice!

They were toys destined only to bob up and down in nothing bigger than a child's bath - but so far they have floated halfway around the world.

The armada of 29,000 plastic yellow ducks, blue turtles and green frogs broke free from a cargo ship 15 years ago.

Since then they have travelled 17,000 miles, floating over the site where the Titanic sank, landing in Hawaii and even spending years frozen in an Arctic ice pack.

And now they are heading straight for Britain. At some point this summer they are expected to be spotted on beaches in South-West England.

While the ducks are undoubtedly a loss to the bath-time fun of thousands of children, their adventures at sea have proved an innvaluable aid to science.

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rubber ducks

The toys have helped researchers to chart the great ocean currents because when they are spotted bobbing on the waves they are much more likely to be reported to the authorities than the floats which scientists normally use.

And because the toys are made of durable plastic and are sealed watertight, they have been able to survive years adrift at the mercy of the elements.

Boxes of the bathtime toys - made in China for the U.S. firm The First Years Inc - were washed overboard in the eastern Pacific Ocean one stormy January night in 1992 and broke open.

In the intervening time an oceanographer, Curtis Ebbesmeyer, has devoted his retirement to tracking the little yellow ducks and their friends over 17,000 miles, and it is he who has predicted that this summer they will land in the

West of England. Mr Ebbesmeyer said: 'We're getting reports of ducks being washed up on America's eastern seaboard.

"It is now inevitable that they will get caught up in the Atlantic currents and will turn up on English beaches.

"Cornwall and the South-West will probably get the first wave of them."

Curtis Ebbesmeyer

Curtis Ebbesmeyer has been tracking the floating plastic ducks around the world's oceans

Mr Ebbesmeyer said the toys will be easy for British beachboardcombers to spot because they have largely faded to white and have the words "The First Years" stamped upon them.

George Bush Snr was still US President when the toys from The First Years Inc. were made in China, packed into a container and put on a ship for the US.

But after falling overboard, the sea water corroded the card-packaging and the toys floated free. They circled the northern Pacific once before being washed up on the Alaskan shore, then all down the West coast of Canada and the US.

Mr Ebbesmeyer saw immediately how valuable the little toys would be to scientific research of the great ocean currents, the engine of the planet's entire climate.

He correctly predicted what many thought was impossible - that thousands of them would end up washed into the Arctic ice near Alaska, and then move at a mile a day, frozen in the pack ice, around their very own North-West Passage to the Atlantic.

It proved true years later and in 2003, the first "Friendly Floatees" were found, frozen and then thawed out, on the eastern seaboard of the U.S. and Canada.

So precious to science are they that the US firm that made them is offering a £50 bounty for finding one.


10 JANUARY 1992: Somewhere in the middle of the Pacific Ocean nearly 29,000 First Years bath toys, including bright yellow rubber ducks, are spilled from a cargo ship in the Pacific Ocean.

16 NOVEMBER 1992: Caught in the Subpolar Gyre (counter-clockwise ocean current in the Bering Sea, between Alaska and Siberia), the ducks take 10 months to begin landing on the shores of Alaska.

EARLY 1995: The ducks take three years to circle around. East from the drop site to Alaska, then west and south to Japan before turning back north and east passing the original drop site and again landing in North America. Some ducks are even found In Hawaii. The National Oceanic and Atmospheric Administration (NOAA) worked out that the ducks travel approximately 50 per pent faster than the water in the current.

1995 - 2000: Some intrepid ducks escape the Subpolar Gyre and head North, through the Bering Straight and into the frozen waters of the Arctic. Frozen into the ice the ducks travel slowly across the pole, moving ever eastward.

2000: Ducks begin reaching the North Atlantic where they begin to thaw and move Southward. Soon ducks are sighted bobbing in the waves from Maine to Massachusetts.

2001: Ducks are tracked in the area where the Titanic sank.

JULY TO DECEMBER 2003: The First Years company offers a $100 savings bond reward for the recovery of wayward ducks from the 1992 spill. To be valid ducks must be sent to the company and must be found in New England, Canada or Iceland. Britain is told to prepare for an invasion of the wayward ducks as well.

2003: A lawyer called Sonali Naik was on holiday in the Hebrides in north-west Scotland when she found a faded green frog on the beach marked with the magic words 'The First Years'. Unaware of the significance of her find she left it on the beach. It was only when she was chatting to other guests at her hotel that she realised what she had seen.

Shark Bite Leads to Reproduction Mystery

Parthenogenesis, the ability of females of some species able to reproduce without the help of male sperm. This feat which is seen in insects, some reptiles and fish may now have been documented twice in shark species. This is amazing. All because a female shark bit an aquarium curator, reacted badly to sedatives and was dissected to find a nearly ready to be born pup in the uterus in a tank without any males of the species. Imagine how many sharks in the wild might have been born to only one mother?
Read the article here.